The present invention relates to lasers and, more particularly, to a resonator structure for the same which includes an arrangement for properly positioning an optical element outside the laser optical cavity.
In its basic aspects, an ion laser is made up of a lasable medium positioned between a pair of optical reflectors which reflect optical radiation emitted by the medium back-and-forth through the same to cause the stimulated emission of optical radiation. Typically, one of the optical reflectors is partially transmissive to permit optical radiation to escape from the laser optical cavity, and thereby form an output beam of coherent radiation.
It is important in achieving appropriate lasing action, that the optical reflectors of the laser be maintained in a selected, rigid and spaced-apart relationship relative to one another. Even slight changes in such relationship can result in power losses, output beam frequency changes, etc. It has therefore become the practice to provide a resonator structure which supports the mounts for the optical reflectors at their spaced apart locations. Such a resonator structure is carefully designed and made to maintain a rigid positional relationship between the optical reflectors, in spite of potential thermal distortions, limited vibrations, etc. Examples of resonator structures following a design which has been found to be particularly suitable, are described in U.S. Pat. Nos. 3,864,029; 3,966,309; 4,143,339; and 4,201,951 in which I am named as a sole or joint inventor. As described in these patents, the resonator structure design includes mounts for the optical reflectors maintained in a desired, predetermined relationship by a plurality of metal alloy rods extending parallel to the optical axis of the laser. Such rods are made of a material having a low coefficient of thermal expansion in the direction of the laser optical axis over the ambient temperature range to which they are expected to be subjected during operation of the laser. The metal alloy sold under the trademark INVAR, which is especially formulated to be dimensionally insensitive to thermal changes, is quite suitable.
Lasers are increasingly being used as sources of coherent radiation in products in which it is desired to maintain a set or closely adjustable relationship between the laser output beam and an optical element which receives it. For example, in eye photocoagulators utilizing laser coherent radiation, the output of an ion laser is typically focused to the receptor end of a fiberoptics strand or bundle. It is important in many of such uses that the relationship of the path of the laser beam relative to the optical element(s) be quite well defined and maintainable.